Process for molding a thermosetting resin

Abstract

A method of molding a thermosetting resin, in particular of the epoxy resin type, in which a first mold is filled with the resin while causing the temperature of the resin to vary in application of a first temperature program, without exceeding the Tg of the resin. After the first mold has been filled, the resin is put under pressure while causing the temperature of the resin to vary in application of a second temperature program, without exceeding Tg, and a drop in the pressure exerted by the resin on the mold is detected with the instant at which this pressure presents a break of slope being identified as the instant t1. A second mold is filled with the thermosetting resin in application of the first temperature program. After the second mold has been filled, the resin is put under pressure in application of the second temperature program until an instant t2 close to t1. As from t2, the temperature of the resin is increased to exceed Tg.

The invention claimed is: 
     
       1. A method of molding a thermosetting resin, comprising, during a first stage:
 filling a first mold with a first thermosetting resin while causing the temperature of the first thermosetting resin to vary in compliance with a first temperature program, without exceeding a glass transition temperature Tg of the first thermosetting resin; and 
 after the first mold has been filled, putting the first thermosetting resin under pressure while causing the temperature of the first thermosetting resin to vary in compliance with a second temperature program, without exceeding the glass transition temperature Tg of the first thermosetting resin, and detecting a drop in the pressure exerted by the first thermosetting resin on the first mold by identifying an instant t1 when the pressure presents a break of slope over time; and 
 in a second stage:
 filling a second mold with a second thermosetting resin that includes a same material as the first thermosetting resin, while causing the temperature of the second thermosetting resin to vary in compliance with the first temperature program; and 
 after the second mold has been filled, putting the second thermosetting resin under pressure while causing the temperature of the second thermosetting resin to vary in compliance with the second temperature program up to an instant t2 that lies in a time interval [t1−10 minutes (min), t1+10 min] or in a time interval [t1−(t1−t0)/2, t1+(t1−t0)/2], where t0 is a timing at which the first mold is filled with the first thermosetting resin, and then from the instant t2, increasing the temperature of the second thermosetting resin so as to exceed the glass transition temperature Tg of the second thermosetting resin. 
 
 
     
     
       2. A method according to  claim 1 , wherein the instant t2 lies in the time interval [t1−10 min, t1+10 min]. 
     
     
       3. A method according to  claim 1 , wherein the second temperature program is an isothermal program. 
     
     
       4. A method according to  claim 1 , wherein, in the second temperature program, the temperature of either the first thermosetting resin or the second thermosetting resin is held at a value lying in the temperature range [Tg−20° C., Tg−10° C.]. 
     
     
       5. A method according to  claim 1 , wherein, at the instant t2, the rate at which the temperature of the second thermosetting resin increases lies in the range 0.56° C./min to 3.3° C./min. 
     
     
       6. A method according to  claim 1 , wherein the first thermosetting resin and the second thermosetting resin include a same epoxy resin material. 
     
     
       7. A method according to  claim 6 , wherein the epoxy resin material possesses at least one of the following properties: being a resin of class 180° C., having improved toughness, or having Tg equal to about 155° C. 
     
     
       8. A method according to  claim 1 , wherein the second mold is analogous or identical to the first mold. 
     
     
       9. A method according to  claim 1 , wherein the duration t1−t0 is 30 minutes. 
     
     
       10. A method according to  claim 1 , wherein the second temperature program is an isothermal program that holds the temperature of the second thermosetting resin constant until, when the instant t2 is reached, the temperature of the second thermosetting resin is increased so as to exceed the glass transition temperature Tg of the second thermosetting resin. 
     
     
       11. A method according to  claim 1 , wherein increasing the temperature of the second thermosetting resin so as to exceed the glass transition temperature Tg of the second thermosetting resin triggers an increase of pressure exerted by the second thermosetting resin on the second mold. 
     
     
       12. A method according to  claim 1 , wherein increasing the temperature of the second thermosetting resin so as to exceed the glass transition temperature Tg of the second thermosetting resin is performed while the second thermosetting resin is polymerizing.